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A U Sheth

Publications and source records attributed to A U Sheth.

5 recordsLinked to original sources
PubMed1982

Free-flow micropuncture study of renal urate transport in the Munich-Wistar rat.

In order to determine the nephron sites of urate reabsorption, the fractional rates of delivery of urate to specific segments of the superficial and deep nephrons were determined by the free-flow micropuncture technique in the Munich-Wistar rat. In nondiuretic control animals, the fractional delivery of urate to the late proximal tubule (34.1 +/- 3.6%), distal tubule (39.0 +/- 6.2%), base (32.6 +/- 3.2%), and tip (32.3 +/- 5.6%) of the papillary collecting duct were not different from one another. In animals in which the extracellular fluid volume was expanded with isotonic saline and in animals infused with the uricosuric diuretic MK-196, the fractional rates of urate delivery to any given nephron segment were significantly higher than in controls. There were no significant differences in either group, however, in the rates of delivery of urate to the specific nephron sites sampled. These studies indicate that urate absorption occurs primarily in the proximal convoluted tubule, but provide no evidence for nephron heterogeneity for urate transport. Expansion of the extracellular fluid volume and the infusion of MK-196 resulted in a higher fractional excretion of urate.

Absorption↗
PubMed1981

Segmental chloride reabsorption during volume expansion and recovery.

Clearance and micropuncture studies were performed in Sprague-Dawley and Munich-Wistar rats to examine the nephron sites of chloride reabsorption in animals undergoing sustained volume expansion (SVE) (10% of body wt) with isotonic saline and in animals in which the extracellular fluid volume was expanded to 10% of body wt over 60 min, after which the sustaining saline volume was abruptly discontinued (recovery) (R). Net sodium and chloride balances were not significantly different in R compared with SVE. The fractional excretion of chloride, however, was significantly lower (2.62 +/- 0.25 vs. 4.18 +/- 0.62%, P less than 0.05). In the Sprague-Dawley rats, chloride delivery to the early distal tubule average 18% in both groups. Chloride delivery to the late distal tubule was significantly lower in R (4.39 +/- 0.79%) than in SVE (8.55 +/- 0.76%, P less than 0.005). In the Munich-Wistar rats, samples were obtained from the late distal tubule and base and tip of the papilla. Chloride delivery to the base did not differ from that to the late distal tubule in either group, but was significantly lower in R compared with SVE. These results indicate that the so-called "post-volume expansion" antinatriuresis is the result, at least in part, of enhanced reabsorption in the distal tubule.

Absorption↗
PubMed1981

Renal handling of gentamicin by the Munich-Wistar rat.

Free-flow micropuncture studies were performed in the Munich-Wistar rat to determine the nephron sites of gentamicin transport. The rats were infused with radiolabeled gentamicin and were volume-expanded with either isotonic sodium chloride or sodium bicarbonate. The fractional delivery of ultrafilterable gentamicin (FD) out of the superficial proximal tubule averaged 75% in both groups of animals. FD to the superficial distal tubule averaged 58.1 +/- 2.1% in saline-infused and 91.6 +/- 5.3% in bicarbonate-infused animals. FD to Henle's loop was 118.2 +/- 8.8 and 124.3 +/- 8.1% in saline- and bicarbonate-infused animals, respectively. FD to the base and tip of the papilla was not significantly different between the two groups and averaged 97.3 +/- 2.9 and 96.1 +/- 3.0% in the saline-infused and 100.5 +/- 2.6 and 94.3 +/- 2.8% in the bicarbonate-infused animals. FD to the base of the papilla was significantly lower than that to the loop of Henle in both groups. These studies indicate that gentamicin undergoes net reabsorption in juxtamedullary proximal tubules. Expansion of the extracellular fluid volume with saline or bicarbonate results in differing rates of gentamicin delivery to the superficial distal tubule but not to the base of the papilla. These findings suggest a significant degree of nephron heterogeneity for gentamicin transport in the rat kidney.

Animals↗
PubMed1980

Secretion of urate in the proximal convoluted tubule of the rat.

In order to examine the transepithelial secretory flux of urate in the rat proximal tubule, simultaneous perfusions of capillaries and lumens were performed. The capillary perfusate contained [2-14C]urate in concentrations of 0.305--2.94 mM. The secretory flux of urate increased as the concentration of urate in the capillary perfusion solution was increased from 0.305 to 1.235 mM but tended toward a plateau at higher concentrations. An apparent Km of 0.41 mM and Vmax of 4.7 pmol . min-1 . mm-1 were calculated from the observed net flux and an estimated passive permeability coefficient of 0.725 pmol . min-1 . mm-1. The addition of probenecid (10(-4) M) to the capillary perfusion solution inhibited urate secretion in a manner consistent with that of a competitive inhibitor. The addition of p-chloromercuribenzoate (10(-4) M) to the capillary perfusion solution inhibited the Vmax but not the Km, suggesting a non-competitive type of inhibition. These data provide the first estimates of the apparent transport constants for urate secretion in the rat proximal tubule determined in vivo. Urate secretion is mediated by a saturable carrier-mediated system. This carrier is not affected by the presence or absence of potassium in the perfusion solution but can be inhibited by the addition of either probenecid or p-shloromercuribenzoate.

Animals↗